The invention relates in general to a means for reciprocally moving an apparatus along a guided path, and in particular to means for connecting a reciprocal apparatus to a threadable connection on a lead screw for minimizing wear on the threadable connection.
In many instruments and assembly, it is necessary to provide true linear reciprocal movement of an element along a given path in order to perform a particular function. For instance, in apparatus for making orthophotos, such as shown in U.S. Pat. No. 3,694,072, it is necessary that a scanning element be moved precisely in linear paths in order to function properly. Positive guiding thereof is provided by a pair of spaced parallel guide rails or other similar means, which guide rails are received by collars of the scanning element platform. A drive means for moving the platform along the guide rails is provided by a ball or lead screw which is rotatable by a motor, and a conventional threaded connection that is connected to the platform and translates the rotational movement of the lead screw to linear motion. Since the threaded connection is rigidly connected to the platform, the lead screw must be made exactly parallel to the guide rails in order to prevent excessive wear on the threaded connection. Exact parallelism is not of course possible in practice, therefore in the portion of the path of movement of the threaded connection near the journalled ends of the lead screw, excessive wear of the threaded connection can result.
According to the present invention, means are provided for connecting a threaded connection associated with a lead screw to a positively guided platform or other apparatus to be linearly reciprocated thereby that minimizes the wear of the threaded connection, thus resulting in longer life thereof. According to the present invention means connecting the positively guided reciprocal apparatus and a threaded connection are provided that do not allow relative movement therebetween in the direction of movement of the apparatus or twisting relative movement (which movements would result in inaccurate operation of the apparatus), yet allow limited relative movement between the apparatus and connection in directions transverse to the direction of movement of the apparatus. The limited movement provided is normally only on the order of a few thousandths of an inch, however, it is enough to prevent excessive stresses being transferred to the threaded connection as a result of a small deviation from parallelism of the lead screw and the guide rails or the like for guiding the apparatus.
According to the present invention, the means for connecting the threadable connection to the apparatus includes a pair of rigid plate members each having an opening therethrough for receipt of the lead screw, and a pair of U-shaped members of relatively thin gauge steel. One of the rigid plate members is connected to the threaded connection, and the other is connected to the apparatus. The U-shaped members, which each include two plate-legs, each with a free end, connected together by a plate cross-member, have the free ends of the legs thereof operatively connected to the rigid plate members, one U-shaped member connected to each plate member. The U-shaped members are connected together at their cross-members, with the cross-members in face-to-face relationship, cooperating openings being formed in the cross-members for receipt of the lead screw. The tensile and compressive rigidity of the legs of the U-shaped members prevents relative movement between the apparatus and the threaded connection in the direction of movement of the apparatus, rigid locked-screw and pin or the like connections between the U-shaped members' legs and the rigid plate members prevents relative twisting, and the relative flexibility of the legs of the U-shaped members to force components transverse to the planes of the legs thereof allows limited relative movement between the threaded connection and the apparatus in directions transverse to the direction of movement of the apparatus. The coupling flexes in response to such transverse forces that are large enough that they would cause excessive wear if there was no movement allowed.
It is the primary object of the present invention to provide means for minimizing the wear of the component parts of a lead screw-threaded connection drive means for positively reciprocally guided apparatus. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.